docs: def get_area(self):
          '''
          Calculates the area of the fault (km ** 2.) as the product of length
          (km) and downdip width (km)
          '''
          d_z = self.lower_depth - self.upper_depth
          self.downdip_width = d_z / np.sin(self.dip * np.pi / 180.)
          self.surface_width = self.downdip_width * np.cos(self.dip *
                                                           np.pi / 180.)
          self.area = self.length * self.downdip_width
          return self.area